Becoming older I'm getting more sensitive to cold and can't sleep properly without sufficient insulation from the bottom.
My usual setup for years has been just a single Thermarest Prolite Plus L (R-value 3.2, 0,88kg)
In more recent years I've added a Z-style CCF pad (R-value 1.9, 0,34kg)
This setup works fine so far for winter hiking, but packsize and weight poses some issue.

So last autumn I purchased an older model with single valve Exped DownMat HL Winter LW (R-value 7, 0.7kg)
This pad packs really small and is comfortable to sleep on.
But I was cold during the night, using the same down sleeping bag as always (an older Exped Swan 800g).
I tried to improve the setup by adding the CCF pad, and I still was cold.
I also tried to use double down sleeping bags and still was cold from the bottom.
I went back to using the Thermarest Prolite plus and the CCF and I slept just fine.

My theory is, the sleeping bag is wider than the DownMat pad, so alongside the left&right side of the pad the less insulated bottom side of the bag gets exposed and this seems to be the area where the cold creeps in.
But then, I also have the impression that pad itself doesnt insulate as well as the sheer numbers would suggest.

So now my question is, whats your experience using a DownMat?
Does it work for you as advertised ("made for hardest winter expeditions in severe cold")?